Weakly bound s1/2 neutrons in the many-body pair correlation of neutron drip line nuclei -: art. no. 064302

With a simplified model in the Hartree-Fock-Bogoliubov (HFB) approximation, the behavior of weakly bound s(1/2) neutrons in the many-body pair correlation is studied by solving the HFB equation in coordinate space with the correct asymptotic boundary conditions. It is shown that in one-neutron pickup reactions on the even-even neutron-drip-line nuclei, which contain loosely bound s(1/2) neutrons, the strength of the s(1/2) neutron can appear both at a discrete state and in the low-energy continuum spectra, with comparable strength. When there is no weakly bound discrete state, the continuum spectra may exhibit a sharp peak just above E-x=\lambda\, which originates from the resonantlike behavior of the upper component of the HFB radial wave function, u(s1/2)(E-qp,r). This resonantlike behavior may be directly observed as an s-wave resonance close to E-x=/lambda\ in neutron-scattering experiments on those nuclei. It is also shown that a very large root-mean-square radius of loosely bound s(1/2) neutrons may appear also in the presence of many-body pair correlation, since the effective pair gap in weakly bound neutron orbits with low l values is much reduced.